This invention relates to an apparatus for making crisscross-wound layers to form fiber-reinforced, rotationally symmetrical wound bodies. The apparatus comprises a rotatable winding mandrel as well as a carriage travelling back and forth parallel to the mandrel axis. On the carriage there is mounted a thread guiding device and a pivotal thread laying mechanism which is provided with a laying roller or, in case of alternating thread laying, with a laying roller pair for depositing on the mandrel a plurality of threads impregnated with synthetic resin.
Wound bodies formed of threads, such as glass fiber, Kevlar fiber or carbon fiber threads and an adhesive, such as synthetic resin are formed, as a rule, by circumferentially wound or crisscross-wound layers.
The circumferentially wound layers, wherein the threads are deposited substantially in a circumferential direction on the winding mandrel with a relatively small feed of the carriage supporting the laying roller, result in a high strength in the circumferential direction of the body.
The crisscross-wound layers, wherein the threads are deposited on the mandrel in steep helices with a relatively large feed of the carriage supporting the laying roller, result in a high strength of the wound body in the axial direction as well as in a high bending strength. The helical crisscross windings are usually deposited in laying angles of approximately .alpha.=45.degree. to 90.degree., as measured in the circumferential direction of the mandrel. Since helical windings have to be applied in both directions, positive and negative winding angles appear.
In the continuous crisscross winding process the mandrel is rotated with an approximately constant speed whereas the carriage which supports the thread laying roller is reciprocated along the winding mandrel. In this manner, there is obtained, during forward travel of the carriage, a thread laying helix with a winding angle +.alpha. and during the return travel of the carriage there is obtained a winding angle of -.alpha..
At the ends of the winding mandrel the thread or threads pass over the end caps of the winding mandrel. During this occurrence the thread laying roller has to pivot through an angle of 2.alpha. or, in case of alternating laying by means of a thread laying roller pair, the rollers have to pivot through an angle of 2(90.degree.-.alpha.).
A thread laying system including a pivotal laying roller pair for an individual thread is disclosed in U.S. Pat. No. 4,359,356 issued Nov. 16, 1982. As shown in FIG. 5 of the patent, the thread is advanced approximately perpendicularly to the winding mandrel axis to a guide roller which is mounted on the outer circumference of a frame affixed to a carriage. The frame is provided with an aperture in which a hollow shaft oriented towards the winding mandrel is pivotally mounted. The thread laying roller pair is carried at the end of the hollow shaft. The thread running from the guide roller passes through the hollow shaft and is alternately deposited on the winding mandrel by one and the other laying roller.
In case of thread laying with a single laying roller as well as in case of thread laying with a laying roller pair, the pivotal motion of the roller or rollers at the end of the mandrel as well as the correct positioning of the roller or rollers during thread laying is effected solely by the tension of the running thread. Such an arrangement, however, is stable in principle only if the pivotal system includes a device which ensures that the threads always run onto the laying roller at the same location. Only then it is ensured that the running thread always sets the rollers in the correct orientation by means of the thread tension. In the simplest case such a stabilizing device is a groove provided in the laying roller for each thread. These grooves ensure that the threads run correctly onto the laying roller.
In case of laying several threads, between the grooves of the laying roller webs are necessarily provided which prevent the threads from sufficiently "flattening out" (spreading) on the laying roller. This limits the maximum width-wise expansion of the threads on the winding mandrel. Thus, the webs are "reproduced" on the winding mandrel, so that instead of a desired smooth surface configuration the deposited layers have a wavy surface.